WO2012033014A1

WO2012033014A1 - Liquid crystal display device

Info

Publication number: WO2012033014A1
Application number: PCT/JP2011/070009
Authority: WO
Inventors: 仲西　洋平; 真伸水▲崎▼; 健史野間; 祐一郎山田
Original assignee: シャープ株式会社
Priority date: 2010-09-08
Filing date: 2011-09-02
Publication date: 2012-03-15
Also published as: CN103109229A; CN103109229B; US20130169906A1

Abstract

The present invention relates to a liquid crystal display device which has a polymer layer that is formed on an alignment film and controls the alignment of liquid crystal molecules adjacent thereto. The polymer layer is formed by polymerizing monomers that are added into a liquid crystal layer, and the monomers are compounds represented by general formula (I). P¹-A¹-(Z¹-A²)_n-P² (I) (In the formula, P¹ and P² may be the same as or different from each other and each represents an acrylate group or a methacrylate group; in cases where there are a plurality of Z¹ moieties, the Z¹ moieties may be the same as or different from each other and each represents COO, OCO or O, or alternatively represents that A¹ and A² or A² and A² are directly bonded with each other; a hydrogen atom may be substituted by a halogen atom, a methyl group, an ethyl group or a propyl group; and A¹ and A² may be the same as or different from each other and each represents a specific phenanthrene group.) The light source of a backlight is composed of at least one light emitting diode, and each light emitting diode substantially emits only such light that has a wavelength of 400 nm or more.

Description

Liquid crystal display

The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device in which a polymer layer is formed on an alignment film in order to increase the alignment regulating force of the liquid crystal.

Liquid crystal display devices are widely used as display devices such as televisions, personal computers, and PDAs because they are thin, light, and have low power consumption. Particularly in recent years, the size of liquid crystal display devices has been rapidly increasing, as represented by liquid crystal display devices for television. In increasing the size, a multi-domain vertical alignment mode (MVA) that can be manufactured with a high yield even in a large area and has a wide viewing angle is preferably used. In the multi-domain vertical alignment mode, the liquid crystal molecules are aligned perpendicular to the substrate surface when no voltage is applied to the liquid crystal layer, so that a high contrast ratio is obtained compared to the conventional TN mode (TN: Twisted Nematic). be able to.

However, since the MVA mode uses ribs (projections), the aperture ratio is lowered, and as a result, white brightness is lowered. In order to remedy this drawback, the rib arrangement interval may be sufficiently widened. However, since the number of ribs that are alignment regulating structures is reduced, it takes time to stabilize the alignment even when a predetermined voltage is applied to the liquid crystal. This causes a problem that the response speed becomes slow. In order to improve such problems and to enable high brightness and high-speed response, a pretilt angle providing technique using a polymer (hereinafter also referred to as a PSA (Polymer Sustained Alignment) layer) has been proposed ( For example, see Patent Documents 1 to 5.) In the PSA technology, a liquid crystal composition in which polymerizable components such as monomers and oligomers (hereinafter abbreviated as monomers) are mixed between liquid crystals is sealed between substrates, and a voltage is applied between the substrates to tilt the liquid crystal molecules. In this state, monomers and the like are polymerized to form a polymer. Thereby, even if the voltage application is removed, the liquid crystal has a predetermined pretilt angle, and the liquid crystal alignment azimuth can be defined. Polymerization of monomers and the like is performed by heat or light (ultraviolet) irradiation. By using the PSA technique, a rib is not required and the aperture ratio is improved. At the same time, a pretilt angle smaller than 90 ° is given over the entire display area, and high-speed response is possible.

JP 2003-307720 A JP 2009-132718 A International Publication No. 2009/118086 Pamphlet Chinese Patent No. 101008784 US Patent Application Publication No. 2008/179565

However, as a result of studies by the present inventors, a liquid crystal layer composition containing a liquid crystal material, a monomer, a polymerization initiator, and the like is injected between a pair of substrates, and a polymerization reaction is caused under a predetermined condition to cause an upper surface of the alignment film. Even if a polymer layer for increasing the orientation regulating power is formed, the conventional PSA technology may cause “burn-in” that remains thin even if the displayed image is switched when the same pattern is displayed for a long time. there were. One of the causes of image sticking is that a DC offset voltage is generated inside the cell due to the presence of a charged substance (ion, radical generator, etc.), so that a desired liquid crystal can be obtained even when a voltage is applied in the liquid crystal layer. It is mentioned that the orientation state is not obtained.

The inventors of the present invention have studied various methods for preventing image sticking, and have focused on a polymer layer (PSA layer) for improving the alignment regulating force formed on the alignment film.

FIG. 8 is a graph showing an example of the absorbance (au) of the monomer. As shown in FIG. 8, the following chemical formula (2):

Is a monomer that generates radicals upon irradiation with light having a wavelength of 320 nm or less. However, a substrate having an alignment film on a surface generally used for a liquid crystal display device tends to hardly transmit light having a wavelength of less than 330 nm due to the influence of a polymer main chain and side chains constituting the alignment film. On the other hand, many high-pressure mercury lamps used as general light sources irradiate light having a small emission line peak at 313 nm and a large emission intensity at 330 nm or more. Therefore, in order to sufficiently photopolymerize the reference monomer, it is necessary to irradiate ultraviolet light of 313 nm for a long time or a plurality of times. However, when such ultraviolet light is irradiated for a long time or a plurality of times, deterioration of components of the liquid crystal display device (for example, an alignment film and a liquid crystal layer) proceeds, and defects such as image sticking may occur. On the other hand, when UV irradiation is performed for a short time to stop the progress of the deterioration of the alignment film and the liquid crystal layer, the monomer is not sufficiently polymerized and an incomplete PSA layer is formed, causing defects such as image sticking. There is. Therefore, for example, as shown in FIG. 8, the present inventors have the following chemical formula (3) having absorption characteristics even for light having a wavelength of 330 nm or more;

Focusing on the fact that the light utilization efficiency can be increased by using a phenanthrene-based monomer represented by the following formula, it has been found that a stable PSA layer can be formed even in a short time and with a single irradiation. As a result, it has been found that it is possible to make it difficult to generate a residual DC voltage in the liquid crystal layer, and to reduce display burn-in.

However, as a result of further studies by the present inventors, it has become clear that the following problems are newly generated even when the phenanthrene-based monomer is used. The problem is that after a series of polymerization reactions in which a liquid crystal layer composition containing a liquid crystal material, a monomer, a polymerization initiator, etc. is injected between a pair of substrates and light irradiation is completed, an unreacted monomer is present in the liquid crystal layer. And the point where the polymerization initiator remains, and when the unreacted monomer and the polymerization initiator remain in the liquid crystal layer, for example, the influence of backlight light in a general use mode after completion, Or, due to the influence of the inspection aging process after the assembly process, the unreacted monomer slowly starts the polymerization reaction, and as a result, the shape of the PSA layer formed following the liquid crystal molecules in the alignment state is changed. As a result, defects such as image sticking occur.

In other words, the phenanthrene-based monomer has a wide absorption wavelength range compared to the biphenyl-based monomer, and has an advantage that the speed of the polymerization reaction is high, but on the other hand, against the backlight light used in a general usage mode. It is also clear that, in order to form a new polymer layer, it also includes a factor that increases the probability of occurrence of seizure.

The present invention has been made in view of the above situation, and an object of the present invention is to provide a liquid crystal display device in which image sticking due to residual monomers in a liquid crystal layer hardly occurs.

The inventors of the present invention have studied various methods for preventing burn-in, and have focused on the type of light source used for the backlight. When a general cold cathode fluorescent lamp (CCFL: Cold Cathode Fluorescent Lamp) is used as a light source for the backlight, the light emitted from the CCFL contains ultraviolet light, so the absorption wavelength in the ultraviolet light region. A phenanthrene monomer having a polymerization reaction was found to have undergone a polymerization reaction, and a light emitting diode (LED: Light Emitting Diode) was used as a backlight light source, and the light emitted from the LED was designed not to contain ultraviolet light. As a result, it has been found that the polymerization reaction of the monomer by backlight light can be suppressed.

FIG. 9 is a graph showing an example of emission spectra of CCFLs and LEDs. FIG. 10 is an enlarged graph of 350 to 420 nm in the CCFL emission spectrum of FIG. Since CCFL emits light by exciting mercury, in principle, it has a plurality of small peaks in the vicinity of 313 nm, 365 nm, and 405 nm, that is, in the ultraviolet region. CCFL has a plurality of large peaks in the vicinity of 440 nm, 490 nm, 550 nm, 590 nm, and 610 nm. On the other hand, the LED has a large peak around 450 nm and a gentle peak around 570 nm. The LED does not have a peak in the ultraviolet region.

The light is attenuated by the influence of a member such as a sheet disposed on the front side of the light source. However, for example, although the transmittance of TAC (Tri Acetyl Cellulose) film at 365 nm is 0.1%, the transmittance at 405 nm is 80% or more, and only members such as a sheet positioned in front of the light source It is practically difficult to eliminate seizure. On the other hand, an LED broadens a single spectrum so as to have a predetermined spectrum with a phosphor. Therefore, in principle there is no emission spectrum in the ultraviolet region, and unnecessary wavelengths can be cut.

On the other hand, the present inventors have made various studies on means for preventing the ultraviolet light contained in the backlight light from being irradiated into the liquid crystal layer of the completed liquid crystal display device. We paid attention to the method of preventing ultraviolet light by using the. Specifically, when a burn-in test was performed with a color filter provided on the substrate located on the backlight side of the liquid crystal layer, it was found that the occurrence of burn-in could be suppressed.

FIG. 11 is a graph showing an example of a transmission spectrum of a color filter composed of red, green, and blue. As shown in FIG. 11, the transmittance of the color filter gradually increases from around the wavelength of 350 nm, reaches the vicinity of 500 nm, once decreases to around 580 nm, rises again to around 600 nm, and is almost flat up to 780 nm. A simple graph.

As described above, the color filter exhibits a characteristic of absorbing ultraviolet light having a wavelength of 350 nm or less, and in this case, the polymerization rate of the residual monomer is reduced.

Thus, the present inventors have conceived that the above problems can be solved brilliantly, and have reached the present invention.

That is, one aspect of the present invention is a liquid crystal display device including a pair of substrates, a liquid crystal display panel including a liquid crystal layer sandwiched between the pair of substrates, and a backlight disposed behind the liquid crystal display panel. And at least one of the pair of substrates includes an alignment film that controls alignment of adjacent liquid crystal molecules, and a polymer layer that is formed on the alignment film and controls alignment of adjacent liquid crystal molecules. The layer is formed by polymerization of a monomer added to the liquid crystal layer, and the monomer has the following general formula (I):
P ¹ -A ^1- (Z ¹ -A ² ) _n -P ² (I)
(In the formula, P ¹ and P ² are the same or different and each represents an acrylate group or a methacrylate group. Z ¹ is the same or different when there is a plurality, and is COO, OCO or O, or A ¹ and A ^2. Alternatively, A ² and A ² are directly bonded, and the hydrogen atom may be substituted with a halogen atom, a methyl group, an ethyl group, or a propyl group, and A ¹ and A ² are the same or different. The following chemical formulas (1-1) to (1-4);

(The hydrogen atom may be substituted with a fluorine atom, a chlorine atom, an OCF ₃ group, a CF ₃ group, a CH ₃ group, a CH ₂ F group, or a CHF ₂ group.) Represents. The light source of the backlight is composed of at least one light emitting diode, and each of the light emitting diodes emits only light having a wavelength of substantially 400 nm or more (hereinafter referred to as a liquid crystal display device). , Also referred to as a first liquid crystal display device of the present invention.

According to another aspect of the present invention, a liquid crystal display panel including a pair of substrates, a liquid crystal layer sandwiched between the pair of substrates, and a backlight disposed behind the liquid crystal display panel. In the display device, at least one of the pair of substrates includes an alignment film that controls alignment of adjacent liquid crystal molecules, and a polymer layer that is formed on the alignment film and controls alignment of adjacent liquid crystal molecules, The polymer layer is formed by polymerization of a monomer added to the liquid crystal layer, and the monomer has the following general formula (I):
P ¹ -A ^1- (Z ¹ -A ² ) _n -P ² (I)
(In the formula, P ¹ and P ² are the same or different and each represents an acrylate group or a methacrylate group. Z ¹ is the same or different when there is a plurality, and is COO, OCO or O, or A ¹ and A ^2. Alternatively, A ² and A ² are directly bonded, and the hydrogen atom may be substituted with a halogen atom, a methyl group, an ethyl group, or a propyl group, and A ¹ and A ² are the same or different. The following chemical formulas (1-1) to (1-4);

(The hydrogen atom may be substituted with a fluorine atom, a chlorine atom, an OCF ₃ group, a CF ₃ group, a CH ₃ group, a CH ₂ F group, or a CHF ₂ group.) Represents. And a substrate closer to the backlight among the pair of substrates has a plurality of color filters, and each of the plurality of color filters substantially has a wavelength of 350 nm or more. A liquid crystal display device that transmits only light (hereinafter also referred to as a second liquid crystal display device of the present invention).

Hereinafter, the first and second liquid crystal display devices of the present invention will be described in detail.

In this specification, “front” indicates a direction in which the observer is positioned when the observer looks at the liquid crystal display screen in a general usage mode, and “backward” indicates a general usage mode in the viewer The direction in which the liquid crystal display device is located when the liquid crystal display screen is viewed is shown.

At least one of the pair of substrates included in the first and second liquid crystal display devices of the present invention has an alignment film that controls alignment of adjacent liquid crystal molecules. In the present invention, the alignment film may be either one not subjected to alignment treatment or one subjected to alignment treatment. Examples of the alignment treatment means for performing the alignment treatment include rubbing treatment and photo-alignment treatment.

At least one of the pair of substrates included in the first and second liquid crystal display devices of the present invention has a polymer layer that is formed on the alignment film and controls alignment of adjacent liquid crystal molecules, and the polymer layer includes a liquid crystal It is formed by polymerization of the monomer added in the layer. By forming the polymer layer, the initial inclination of the liquid crystal molecules adjacent to the alignment film and the polymer layer can be tilted in a certain direction even if the alignment film is not subjected to alignment treatment. For example, when a polymer layer is formed by polymerizing a monomer in a state where the liquid crystal molecules are pretilt aligned, the polymer layer is pretilt with respect to the liquid crystal molecules regardless of whether or not the alignment film is aligned. It is formed in a form having a structure to be oriented.

The monomer is a compound represented by the general formula (I), and the condensed aromatic ring structure represented by the chemical formulas (1-1) to (1-4) has a characteristic of absorbing light up to nearly 370 nm. Have. As a result, the light utilization efficiency can be increased, the PSA layer can be sufficiently formed even in a short time and once irradiation, and the residual DC voltage in the liquid crystal layer can be hardly generated. In addition, since light irradiation for a short time is sufficient, deterioration of components due to light irradiation for a long time can be prevented, and the reliability of the liquid crystal display device can be improved.

In the first liquid crystal display device of the present invention, the light source of the backlight includes at least one light emitting diode, and each of the light emitting diodes emits only light having a wavelength of substantially 400 nm or more. That is, in the first liquid crystal display device, an LED is used instead of the CCFL generally used as a backlight light source, and an LED that does not substantially irradiate ultraviolet light having a wavelength of less than 400 nm is selected as the LED. It is a form made. By using such a light source, the polymerization reaction of the monomer does not proceed in a general usage mode after completion of the liquid crystal display device, so that the occurrence of image sticking can be suppressed. From the viewpoint of obtaining the effect of the present invention more reliably, it is preferable that the light emitting diode irradiates only light having a wavelength of substantially 420 nm or more. The wavelength range emitted from the light emitting diode can be changed depending on the type and thickness of the phosphor. For example, a light source that emits light having a wavelength of 405 nm can be obtained using an InGaAs light emitting diode. In principle, the light converted by the phosphor is light having a longer wavelength than the emitted light.

In the second liquid crystal display device of the present invention, a substrate closer to the backlight among the pair of substrates has a plurality of color filters, and each of the plurality of color filters is substantially 350 nm or more. Transmits only light having a wavelength. Preferably, each of the color filters of the plurality of colors substantially transmits only light having a wavelength of 420 nm or more. In this specification, the “color filter” refers to a filter that can transmit only a specific wavelength component. For example, the “red color filter” transmits a wavelength component having a dominant wavelength in the range of 605 to 700 nm, and the “green color filter” transmits a wavelength component having a dominant wavelength in the range of 500 to 560 nm. The “blue color filter” transmits a wavelength component having a dominant wavelength in the range of 435 to 480 nm. The color filters for each color transmit only the wavelength component of each color and reflect or absorb the other wavelength components. Therefore, by arranging the color filter for each color between the liquid crystal layer and the backlight, ultraviolet light can be obtained. Can be effectively prevented from being irradiated into the liquid crystal layer. By using the color filter in this manner, the polymerization reaction of the monomer does not proceed in a general usage mode after completion of the liquid crystal display device, so that the occurrence of image sticking can be suppressed.

The configuration of the liquid crystal display device of the present invention is not particularly limited by other components as long as such components are essential.

A preferable form of the liquid crystal display device of the present invention includes a form in which the features of the first and second liquid crystal display devices of the present invention are combined. That is, in the first liquid crystal display device of the present invention, the substrate closer to the backlight among the pair of substrates has a plurality of color filters, and each of the plurality of color filters is substantially 350 nm. It is preferable to transmit only light having the above wavelength, and more preferably, only light having substantially a wavelength of 420 nm or more is transmitted. In the second liquid crystal display device of the present invention, the light source of the backlight is composed of at least one light emitting diode, and each of the light emitting diodes emits only light having a wavelength of substantially 400 nm or more. More preferably, only light having a wavelength of substantially 420 nm or more is emitted.

According to the liquid crystal display device of the present invention, it is possible to prevent ultraviolet light from being irradiated into the liquid crystal layer of the completed liquid crystal display device, so that the residual monomer while ensuring the advantage of using the phenanthrene monomer It is possible to suppress the occurrence of image sticking due to the occurrence of seizure.

It is a cross-sectional schematic diagram of the liquid crystal display device of Embodiment 1, and shows before a PSA polymerization process. It is a cross-sectional schematic diagram of the liquid crystal display device of Embodiment 1, and shows after a PSA polymerization process. It is a plane schematic diagram of the board | substrate with which the liquid crystal display device of Embodiment 1 is provided, and shows an array board | substrate. It is a plane schematic diagram of the board | substrate with which the liquid crystal display device of Embodiment 1 is provided, and shows a counter substrate. 6 is a schematic plan view illustrating a modification of the pixel electrode of the liquid crystal display device of Embodiment 1. FIG. It is a cross-sectional schematic diagram of the liquid crystal display device of Embodiment 2, and shows before a PSA polymerization process. It is a cross-sectional schematic diagram of the liquid crystal display device of Embodiment 2, and shows after a PSA polymerization process. It is a graph which shows an example of the light absorbency (au) of a monomer. It is a graph which shows an example of the emission spectrum of CCFL and LED. 10 is a graph obtained by enlarging the range of 350 to 420 nm in the emission spectrum of CCFL in FIG. It is a graph which shows an example of the transmission spectrum of the color filter comprised by red, green, and blue. It is a graph which shows an example of the emission spectrum of white LED. It is a graph which shows another example of the transmission spectrum of the color filter comprised by red, green, and blue.

Embodiments will be described below, and the present invention will be described in more detail with reference to the drawings. However, the present invention is not limited to these embodiments.

Embodiment 1
1 and 2 are schematic cross-sectional views of the liquid crystal display device of Embodiment 1. FIG. FIG. 1 shows before the PSA polymerization step, and FIG. 2 shows after the PSA polymerization step. As shown in FIGS. 1 and 2, the liquid crystal display device of Embodiment 1 includes an array substrate 10, a counter substrate 20, and a liquid crystal layer 30 sandwiched between a pair of substrates including the array substrate 10 and the counter substrate 20. A liquid crystal display panel having A backlight 50 is provided behind the liquid crystal display panel. The liquid crystal display device of Embodiment 1 performs display using the light emitted from the backlight 50. That is, the liquid crystal display device of Embodiment 1 is a transmissive liquid crystal display device.

The array substrate 10 includes an insulating transparent substrate 11 made of glass or the like, wiring formed on the transparent substrate 11, pixel electrodes 45, TFTs (Thin Film Transistors) 44, TFTs 44, and pixel electrodes 45. A conductive member such as a contact portion 47 to be connected, a plurality of insulating films 14, and an alignment film 12 are provided. Examples of the material of the pixel electrode 45 include ITO (Indium Tin Oxide). The structure is made efficient by using the same material for the pixel electrode 45 and the conductive member of the contact portion. The alignment film 12 is made of, for example, a polymer compound (polyimide) having a main chain including an imide structure. By performing an alignment process such as a rubbing process or a photo-alignment process on the surface of the alignment film 12, the pretilt angle of the liquid crystal molecules can be oriented vertically or horizontally (initially tilted). The alignment film 12 may be a vertical alignment film or a horizontal alignment film that defines the alignment direction of adjacent liquid crystal molecules without being subjected to alignment treatment. Further, an alignment process may be further performed on the vertical alignment film or the horizontal alignment film. An insulating film 14 is formed between the TFT 44 and the pixel electrode 45, and the alignment film 12 is formed on the pixel electrode 45 and the insulating film 14 exposed without the pixel electrode 45.

The counter substrate 20 includes an insulating transparent substrate 21 made of glass or the like, a color filter 24, a black matrix 26, a common electrode 25, and an alignment film 22. As the alignment film 22 provided on the counter substrate 20 side, an alignment film having the same characteristics as the alignment film 12 provided on the array substrate 10 side described above can be used.

1 and FIG. 2 show a filter using three color filters of red 24R, green 24G, and blue 24B. However, as long as at least these three colors are included, the type, number, and arrangement order of the colors are not particularly limited. It is not limited. For example, four colors including yellow may be used. An example of a method for producing a color filter is a photolithography method in which a color resist based on a pigment is applied on glass, followed by exposure and development. Specifically, first, a black matrix is formed on the transparent substrate for preventing light leakage of the backlight and preventing color mixture of the color filters. Next, a color resist is applied on the transparent substrate and the black matrix. Next, pattern exposure is performed through a photomask, UV curing is performed, and insolubilization is performed. Next, unnecessary portions of the color resist are removed with a developer, and then cured by baking. The above series of steps is repeated for the number of colors of the color filter. Subsequently, an ITO film serving as a common electrode is formed on the color filter and the black matrix by using a sputtering method.

The liquid crystal layer 30 is filled with a liquid crystal material. The type of liquid crystal material is not particularly limited, and any of those having a positive dielectric anisotropy and those having a negative dielectric anisotropy can be used, and can be appropriately selected according to the display mode of the liquid crystal. it can. For example, in a twisted nematic (TN) mode in which the liquid crystal layer is twisted in the thickness direction, a liquid crystal material having positive dielectric anisotropy is used, and the liquid crystal molecules are aligned horizontally with respect to the substrate surface. In in-plane switching (IPS: In-Plane Switching or FFS: Fringe-Field Switching) mode in which a lateral electric field is applied to the liquid crystal layer, a liquid crystal material having positive or negative dielectric anisotropy is used. In the vertical alignment (VA) mode in which the substrate is vertically aligned with the substrate surface, a liquid crystal material having negative dielectric anisotropy is used.

As shown in FIG. 1, one or more monomers 31 are present in the liquid crystal layer 30 before the PSA polymerization step. Then, the monomer 31 starts to be polymerized by the PSA polymerization process, and PSA layers 13 and 23 are formed on the

alignment films

12 and 22 as shown in FIG.

Specifically, the PSA layers 13 and 23 are formed by injecting a composition for forming a liquid crystal layer containing one or more monomers 31 and a liquid crystal material between the array substrate 10 and the counter substrate 20. 30, for example, by irradiating the liquid crystal layer 30 with a certain amount of light to photopolymerize the monomer 31. In FIG. 2, the PSA layers 13 and 23 are shown as being formed on the entire surface of the

alignment films

12 and 22. However, actually, a plurality of PSA layers 13 and 23 may be formed in a dot shape, and the film thickness varies. There may be.

Since the monomer 31 used in Embodiment 1 absorbs light with the monomer 31 alone and generates radicals to start chain polymerization, it is not necessary to administer a polymerization initiator. However, in order to increase the polymerization rate, a polymerization initiator that effectively uses light having a wavelength of 365 nm or more may be added. Examples of such a polymerization initiator include 2,2-dimethoxy-1,2-diphenylethane-1-one.

In the first embodiment, for example, when performing the PSA polymerization step, the liquid crystal layer 30 is irradiated with light in a state where a voltage equal to or higher than the threshold is applied. Since the polymer is formed in such a shape, the PSA layers 13 and 23 to be formed have a structure that functions as an alignment film that defines an initial pretilt angle with respect to liquid crystal molecules even when a voltage is not applied later. It will be.

In the first embodiment, the light irradiation may not be performed in a state where a voltage equal to or higher than the threshold is applied to the liquid crystal layer 30. For example, when the

alignment films

12 and 22 themselves have a property of imparting pretilt alignment to liquid crystal molecules, the PSA layers 13 and 23 formed on the

alignment films

12 and 22 further enhance the alignment stability of the alignment film. Functions as a membrane. By improving the alignment regulating force of the

alignment films

12 and 22, the liquid crystal molecules are more uniformly controlled, the change in alignment with time is reduced, and the display is less likely to be burned. In the first embodiment, the

alignment films

12 and 22 are subjected to alignment treatment, and then light irradiation is performed with a voltage higher than a threshold applied to the liquid crystal layer 30 to form the PSA layers 13 and 23. Thus, a combination of

alignment films

12 and 22 and PSA layers 13 and 23 with higher alignment stability can be obtained.

In the first embodiment, the alignment of the liquid crystal molecules is defined by, for example, a linear slit provided in the pixel electrode 45 included in the array substrate 10 or the common electrode 25 included in the counter substrate 20 (PVA (Patterned Vertical) Alignment) mode). When thin linear slits are formed in the pixel electrode 45 and / or the common electrode 25, the liquid crystal molecules have a uniform alignment toward the linear slits when a voltage is applied. By polymerizing the monomer in a state where the above voltage is applied, a PSA layer that imparts a pretilt angle to the liquid crystal molecules can be formed.

The monomer used in Embodiment 1 is represented by the following general formula (I):
P ¹ -A ^1- (Z ¹ -A ² ) _n -P ² (I)
(In the formula, P ¹ and P ² are the same or different and each represents an acrylate group or a methacrylate group. Z ¹ is the same or different when there is a plurality, and is COO, OCO or O, or A ¹ and A ^2. Alternatively, A ² and A ² are directly bonded, and the hydrogen atom may be substituted with a halogen atom, a methyl group, an ethyl group, or a propyl group, and A ¹ and A ² are the same or different. The following chemical formulas (1-1) to (1-4);

(The hydrogen atom may be substituted with a fluorine atom, a chlorine atom, an OCF ₃ group, a CF ₃ group, a CH ₃ group, a CH ₂ F group, or a CHF ₂ group.) Represents. ). Any condensed aromatic compound represented by

The monomer containing the groups represented by the above chemical formulas (1-1) to (1-4) is a bifunctional monomer, and forms a PSA layer that is more stable than a monofunctional monomer when mixed with a liquid crystal material. be able to. In addition, the phenanthrene-based condensed aromatic compound containing three or more benzene rings represented by the above chemical formulas (1-1) to (1-4) has an absorption wavelength range up to nearly 370 nm. In general, a substrate having an alignment film on the surface used for a liquid crystal display device tends to absorb a large amount of light of less than 330 nm due to the influence of the polymer main chain and side chains constituting the alignment film. By using a monomer containing a group represented by the above chemical formulas (1-1) to (1-4) having a wavelength range, the light use efficiency can be increased, and even a short-time ultraviolet irradiation is sufficient. A PSA layer can be produced.

Other components of the liquid crystal display device according to Embodiment 1 will be described in detail. 3 and 4 are schematic plan views of a substrate provided in the liquid crystal display device of Embodiment 1. FIG. FIG. 3 shows an array substrate, and FIG. 4 shows a counter substrate.

As shown in FIG. 3, each of the pixel electrodes 45 included in the array substrate in the liquid crystal display device of Embodiment 1 has a substantially rectangular shape, and a plurality of pixel electrodes 45 are arranged in a matrix shape or a delta shape to form one display surface. Configure. Note that “substantially rectangular” indicates that a part of the rectangle may include a protruding portion or a cutout portion as shown in FIG. 3.

The array substrate has a plurality of gate signal lines 41, a plurality of source signal lines 42, and a plurality of auxiliary capacitance (Cs) wirings 43 extending in parallel with each other via an insulating film. And the auxiliary capacitance (Cs) wiring 43 extend in parallel to each other and intersect the plurality of source signal lines 42. Further, the gate signal line 41 and the source signal line 42 are connected to the respective electrodes of the thin film transistor (TFT) 44. The TFT 44 is a three-terminal field effect transistor, and has three electrodes including a gate electrode, a source electrode, and a drain electrode in addition to the semiconductor layer. The TFT 44 serves as a switching element that performs pixel drive control. In the first embodiment, one pixel electrode 45 is divided into a plurality of subpixel electrodes, a TFT is provided for each subpixel electrode, and two subpixel electrodes are controlled by one gate signal line. It is good.

As shown in FIG. 4, in the liquid crystal display device according to the first embodiment, the counter substrate 20 includes a light-shielding BM (black matrix) 26, a red color filter 24R that transmits only light of a specific wavelength, and a blue color filter 24R. It has a color filter 24B and a green color filter 24G. BMs 26 are formed in the gaps between the color filters 24, and have a lattice shape as a whole. Each color filter 24 is disposed so as to overlap each pixel electrode of the array substrate.

In the first embodiment, the shape of the pixel electrode may be as shown in FIG. FIG. 5 is a schematic plan view illustrating a modification example of the pixel electrode of the liquid crystal display device according to the first embodiment. The pixel electrode 45 shown in FIG. 5 is an electrode in which a plurality of thin slits are formed from the outer periphery to the inside of a rectangular electrode, and the cross-shaped trunk portion 45a and obliquely outward from both sides of the trunk portion 45a. It comprises a plurality of branch portions 45b that extend. From the viewpoint of improving the viewing angle characteristics, each branch portion 45b preferably extends in a different direction for each region. Specifically, when the extending direction of the cross-shaped trunk portion 45a is 0 °, 90 °, 180 °, and 270 °, the four types extend in the 45 ° direction, the 135 ° direction, the 225 ° direction, and the 315 ° direction, respectively. Branch portion 45b is formed. When the pixel electrode has such a shape, alignment treatment such as rubbing treatment and photo-alignment treatment is not necessary. In addition, when a voltage is applied, the liquid crystal molecules are tilted toward the center of the pixel. Therefore, the alignment of the liquid crystal can be stabilized even when no voltage is applied by forming a PSA layer by exposing in a voltage applied state. As another modification of the first embodiment, there is an MVA (Multi-domain Vertical Alignment) mode in which ribs and slits in electrodes are provided as an alignment control structure to control the alignment of liquid crystal molecules.

In the first embodiment having the pixels shown in FIG. 3 and the like, the

alignment films

12 and 22 may be subjected to any alignment treatment such as rubbing treatment or photo-alignment treatment. The possibility of breakage etc. can be reduced. Further, when the orientation division of the pixel is performed, it can be performed more easily than when the rubbing process is used. Examples of the alignment division include a 4D-RTN (4-Domain Reverse Reverse Twisted Nematic) mode in which the alignment processing directions are made to be orthogonal to each other on a pair of substrates and one pixel is divided into four domains. The corner is greatly improved. In 4D-RTN, high-precision pretilt control is required, but according to the liquid crystal display device of Embodiment 1, a pretilt with excellent stability can be obtained due to the influence of the PSA layer formed on the alignment film. Therefore, even if 4D-RTN is used, sufficient alignment stability can be obtained.

In the liquid crystal display device according to the first embodiment, the array substrate 10, the liquid crystal layer 30, and the counter substrate 20 are stacked in this order from the back surface side to the observation surface side of the liquid crystal display device. A polarizing plate is provided on the back side of the array substrate 10. In addition, a polarizing plate is provided on the observation surface side of the counter substrate 20. A retardation plate may be further arranged for these polarizing plates, and the polarizing plate may be a circularly polarizing plate.

The liquid crystal display device according to the first embodiment is a transmissive liquid crystal display device. The backlight is disposed further on the back side of the array substrate 10 and is disposed so that light is transmitted through the array substrate 10, the liquid crystal layer 30, and the counter substrate 20 in this order. In the case of the reflection / transmission type, the array substrate 10 includes a reflection plate for reflecting outside light. Further, at least in a region where reflected light is used as display light, the polarizing plate of the counter substrate 20 needs to be a circularly polarizing plate provided with a so-called λ / 4 retardation plate.

The type of the backlight is not particularly limited, such as an edge light type or a direct type. In a liquid crystal display device having a small screen, an edge light type that can display with low power consumption with a small number of light sources and is suitable for thinning is widely used.

The type of light source used in Embodiment 1 is a light emitting diode (LED). In the first embodiment, the LED is adjusted so as not to emit light having a wavelength of substantially less than 400 nm. In the first embodiment, the LED is preferably adjusted so as not to emit light having a wavelength of substantially less than 420 nm. For example, a white LED as shown in the graph of FIG. 12 does not emit light having a wavelength of substantially 420 nm or less, which greatly contributes to the reduction of image sticking.

Examples of the member constituting the backlight include a light source, a reflection sheet, a diffusion sheet, a prism sheet, and a light guide plate. In the edge light type backlight, light emitted from the light source enters the light guide plate from the side surface of the light guide plate, is reflected, diffused, etc., and is emitted as planar light from the main surface of the light guide plate, Further, the light passes through a prism sheet or the like and is emitted as display light. In a direct type backlight, light emitted from a light source passes directly through a reflection sheet, a diffusion sheet, a prism sheet, etc. without passing through a light guide plate, and is emitted as display light.

The liquid crystal display device according to Embodiment 1 disassembles a liquid crystal display device (for example, a liquid crystal TV (television)), collects an alignment film, ¹³ C-Nuclear Magnetic Resonance (NMR), mass Analyzing the components of the alignment film, analyzing the components of the PSA layer forming monomer (monomer) present in the PSA layer, and including it in the liquid crystal layer by performing chemical analysis using an analysis method (MS: Mass Spectrometry), etc. The amount of the PSA layer forming monomer (monomer) mixed, the abundance ratio of the PSA layer forming monomer (monomer) in the PSA layer, and the like can be confirmed.

Example 1
A liquid crystal display panel according to Embodiment 1 was actually manufactured, and display burn-in was confirmed. The light source used in Example 1 is an LED having the emission spectrum shown in FIGS. 9 and 10 and has substantially no light having a wavelength of less than 400 nm. On the other hand, in the CCFL having the emission spectrum shown in FIGS. 9 and 10, a very small peak (about 0.04 μW / cm ² ) was observed near 365 nm.

First, a pair of substrates including an array substrate and a counter substrate was prepared, and after a liquid crystal layer forming composition containing a liquid crystal material and a monomer for forming a PSA layer was dropped, it was bonded to the other substrate. The color filter is manufactured on the counter substrate.

In Example 1, the following chemical formula (3) is used as a monomer for forming the PSA layer;

The compound represented by this was used. The compound represented by the chemical formula (3) is a phenanthrene-based bifunctional methacrylate monomer. In Example 1, the liquid crystal layer forming composition was prepared so that the bifunctional phenanthrene monomer represented by the chemical formula (3) was contained by 0.6 wt%.

Next, the liquid crystal layer sandwiched between the pair of substrates is irradiated with 1 J / cm ² of ultraviolet light with a voltage of 10 V AC applied, and a polymerization reaction is performed, whereby the liquid crystal in which the PSA layer is formed on the vertical alignment film Each cell was completed. In addition, the irradiation time of the ultraviolet rays with respect to the liquid crystal cell was 3 minutes. As the ultraviolet light source, a high-pressure mercury lamp (manufactured by Oak Manufacturing Co., Ltd.) was used. Thereafter, no voltage was applied, and light from a light source FHF32-BLB (manufactured by Toshiba Lighting & Technology Corp.) was irradiated for 1 hour. The liquid crystal display panel using the alignment film subjected to the alignment treatment omits the step of applying a voltage.

Subsequently, the completed liquid crystal display panel was placed on the LED backlight for display, and the burn-in rate was measured. In Example 1, the image sticking rate was defined as follows, and quantitative evaluation was performed by the following method. First, the black and white checker pattern was displayed in the display area for 600 hours. Thereafter, a predetermined halftone (gray) was displayed over the entire display area, and the difference β−γ between the brightness β of the area that was white and the brightness γ of the area that was black was black. The burn-in rate was calculated by dividing by the luminance γ of the area. That is, the burn-in rate formula is expressed by the following formula.
Burn-in rate α = ((β−γ) / γ) × 100 (%)

As a result, the burn-in rate of the liquid crystal display panel in Example 1 was 4%.

Comparative Example 1
In order to confirm the difference between the LED and the CCFL, a liquid crystal display panel similar to that in Example 1 was actually manufactured, and the completed liquid crystal display panel was placed on the CCFL backlight having the emission spectrum shown in FIG. The display was performed and the burn-in rate was measured. The definition and evaluation method of the burn-in rate are the same as those in Example 1.

As a result, the burn-in rate of the liquid crystal display panel in Comparative Example 1 was 6%. When CCFL was used, it was shown that the monomer slightly remaining in the liquid crystal layer polymerizes to cause image sticking.

Embodiment 2
The liquid crystal display device of Embodiment 2 is in the form of a color filter on array (COA) in which color filters are formed on an array substrate instead of a counter substrate, and the light source is not limited to LEDs. The same as in the first embodiment.

6 and 7 are schematic cross-sectional views of the liquid crystal display device according to the second embodiment. FIG. 6 shows before the PSA polymerization step, and FIG. 7 shows after the PSA polymerization step. As shown in FIGS. 6 and 7, in the second embodiment, the color filter 24 and the black matrix 26 are formed on the array substrate 10. More specifically, a TFT 44 and a bus line (not shown) are disposed on an insulating transparent substrate 11 made of glass or the like, and a black matrix 26 and a color filter are formed thereon via an insulating film (not shown). 24 is arranged. In some cases, another insulating film may be provided on the color filter 24. The black matrix may be provided only on the counter substrate side. A pixel electrode 45 is disposed at a position overlapping the color filter 24. The pixel electrode 45 and the TFT 44 are connected through a contact portion 47 formed in the color filter 24. When there is an insulating film on the pixel electrode 45 and on the color filter 24 where the surface is exposed without the pixel electrode 45 or on the color filter 24, the alignment film 12 is formed on the insulating film. FIGS. 6 and 7 show a color filter using three color filters of red 24R, green 24G, and blue 24B. However, in the second embodiment, the color filter emits light having a wavelength substantially less than 350 nm. As long as a filter that does not transmit light is selected, the type, number, and arrangement order of colors are not particularly limited. In the second embodiment, it is more preferable that the color filter does not transmit light having a wavelength of substantially less than 420 nm. For example, when a color filter having a characteristic of absorbing light having a wavelength of less than 420 nm as shown in the graph of FIG. 13 is used, light having a wavelength in the ultraviolet region is almost eliminated, thereby reducing the occurrence of image sticking. Contribute greatly.

According to the color filter on array, the problem of misalignment due to the pixel electrode and the color filter being formed on different substrates is solved.

The kind of light source of the backlight 50 used in Embodiment 2 is a light emitting diode (LED) or a cold cathode tube (CCFL).

Example 2
A liquid crystal display panel according to Embodiment 2 was actually manufactured and display burn-in was confirmed. The light source used in Example 2 is a CCFL having an emission spectrum shown in FIGS. 9 and 10 and slightly contains ultraviolet light.

First, a pair of substrates comprising an array substrate and a counter substrate is prepared, and after dropping a composition for forming a liquid crystal layer containing a liquid crystal material and a monomer for forming a PSA layer represented by the chemical formula (3), the other substrate Bonding to the substrate was performed. The color filter is fabricated on the array substrate. The color filter used in Example 2 has the transmission spectrum shown in FIG. 11 and does not transmit light having a wavelength of substantially less than 350 nm.

Next, the liquid crystal layer sandwiched between the pair of substrates is irradiated with 3 J / cm ² of ultraviolet light with a voltage of 10 V AC applied, and a polymerization reaction is performed, whereby the PSA layer is formed on the vertical alignment film. Each cell was completed. In addition, the irradiation time of the ultraviolet rays with respect to the liquid crystal cell was 3 minutes. As the ultraviolet light source, a high-pressure mercury lamp (manufactured by Oak Manufacturing Co., Ltd.) was used. Thereafter, no voltage was applied, and light from a light source FHF32-BLB (manufactured by Toshiba Lighting & Technology Corp.) was irradiated for 1 hour. The liquid crystal display panel using the alignment film subjected to the alignment treatment omits the step of applying a voltage.

Subsequently, the completed liquid crystal display panel was placed on a CCFL backlight for display, and the burn-in rate was measured. The definition and evaluation method of the burn-in rate are the same as those in Example 1.

As a result, the burn-in rate of the liquid crystal display panel in Example 2 was 5%.

Example 3
A liquid crystal display panel according to Embodiment 2 was actually manufactured and display burn-in was confirmed. The light source used in Example 3 is an LED having the emission spectrum shown in FIG. 9 and FIG. 10, and has substantially no light having a wavelength of less than 400 nm.

First, a pair of substrates comprising an array substrate and a counter substrate is prepared, and after dropping a composition for forming a liquid crystal layer containing a liquid crystal material and a monomer for forming a PSA layer represented by the chemical formula (3), the other substrate Bonding to the substrate was performed. The color filter is fabricated on the array substrate. The color filter used in Example 3 has the transmission spectrum shown in FIG. 11 and does not transmit light having a wavelength of substantially less than 350 nm.

Subsequently, the completed liquid crystal display panel was placed on the LED backlight for display, and the burn-in rate was measured. The definition and evaluation method of the burn-in rate are the same as those in Example 1.

As a result, the burn-in rate of the liquid crystal display panel in Example 3 was 3%.

The present application claims priority based on the Paris Convention or the laws and regulations in the country to which the transition is based on Japanese Patent Application No. 2010-201210 filed on September 8, 2010. The contents of the application are hereby incorporated by reference in their entirety.

10: Array substrate 11, 21: Transparent substrate 12, 22: Alignment film 13, 23: PSA layer (polymer layer)
14: Insulating film 20: Counter substrate 24: Color filter 24R: Red (R) color filter 24G: Green (G) color filter 24B: Blue (B) color filter 25: Common electrode 26: Black matrix 30: Liquid crystal Layer 31: Monomer 41: Gate signal line 42: Source signal line 43: Auxiliary capacitance (Cs) wiring 44: TFT
45: Pixel electrode 47: Contact part 50: Backlight

Claims

A liquid crystal display device comprising a pair of substrates, a liquid crystal display panel comprising a liquid crystal layer sandwiched between the pair of substrates, and a backlight disposed behind the liquid crystal display panel,
At least one of the pair of substrates has an alignment film that controls alignment of adjacent liquid crystal molecules, and a polymer layer that is formed on the alignment film and controls alignment of adjacent liquid crystal molecules,
The polymer layer is formed by polymerization of a monomer added to the liquid crystal layer,
The monomer has the following general formula (I):
P 1 -A 1- (Z 1 -A 2 ) n -P 2 (I)
(In the formula, P 1 and P 2 are the same or different and each represents an acrylate group or a methacrylate group. Z 1 is the same or different when there is a plurality, and is COO, OCO or O, or A 1 and A 2. Alternatively, A 2 and A 2 are directly bonded, and the hydrogen atom may be substituted with a halogen atom, a methyl group, an ethyl group, or a propyl group, and A 1 and A 2 are the same or different. The following chemical formulas (1-1) to (1-4);

(The hydrogen atom may be substituted with a fluorine atom, a chlorine atom, an OCF 3 group, a CF 3 group, a CH 3 group, a CH 2 F group, or a CHF 2 group.) Represents. )
A compound represented by
The light source of the backlight comprises at least one light emitting diode,
All of the light emitting diodes emit only light having a wavelength of substantially 400 nm or more.
A liquid crystal display device comprising a pair of substrates, a liquid crystal display panel comprising a liquid crystal layer sandwiched between the pair of substrates, and a backlight disposed behind the liquid crystal display panel,
At least one of the pair of substrates has an alignment film that controls alignment of adjacent liquid crystal molecules, and a polymer layer that is formed on the alignment film and controls alignment of adjacent liquid crystal molecules,
The polymer layer is formed by polymerization of a monomer added to the liquid crystal layer,
The monomer has the following general formula (I):
P 1 -A 1- (Z 1 -A 2 ) n -P 2 (I)
(In the formula, P 1 and P 2 are the same or different and each represents an acrylate group or a methacrylate group. Z 1 is the same or different when there is a plurality, and is COO, OCO or O, or A 1 and A 2. Alternatively, A 2 and A 2 are directly bonded, and the hydrogen atom may be substituted with a halogen atom, a methyl group, an ethyl group, or a propyl group, and A 1 and A 2 are the same or different. The following chemical formulas (1-1) to (1-4);

(The hydrogen atom may be substituted with a fluorine atom, a chlorine atom, an OCF 3 group, a CF 3 group, a CH 3 group, a CH 2 F group, or a CHF 2 group.) Represents. )
A compound represented by
Of the pair of substrates, the substrate closer to the backlight has a plurality of color filters,
All of the color filters of the plurality of colors transmit only light having a wavelength of substantially 350 nm or more.
Of the pair of substrates, the substrate closer to the backlight has a plurality of color filters,
2. The liquid crystal display device according to claim 1, wherein each of the plurality of color filters transmits only light having a wavelength of substantially 350 nm or more.
The light source of the backlight comprises at least one light emitting diode,
3. The liquid crystal display device according to claim 2, wherein each of the light emitting diodes emits only light having a wavelength of substantially 400 nm or more.
5. The liquid crystal display device according to claim 1, wherein each of the light emitting diodes emits only light having a wavelength of substantially 420 nm or more.
4. The liquid crystal display device according to claim 2, wherein each of the plurality of color filters transmits only light having a wavelength of substantially 420 nm or more.